Chp. 1
Speed of sound: 1130ft/se 345m/s, wavelength=c/f
- Harmonics: integer multiples.  Octaves: 2:1 btwn frequencies
Equal Temperament - Tune semitones as a geometric series
Calculating pitches of notes: start	pitch*2^(semitones/12)
Frequency Bands: 3rd octave filter on A440: center freq 440, 3dB on both sides is Fc*2^1/3
Chp. 2
- Ratios closer to human perception than linear numbers
- SPL=20log10(P/Pref) dB
Chp. 3
- Free field: sound travels in straight lines unimpeded.  unreflected, unabsorbed, undeflected, undiffracted, no resonance.  Allows understanding of waves in undisturbed state.  
- Sound divergence: Further from source, more it behaves like point source.  Uniform intensity: critical distance, reverberant level.  Uniform intensity in all directions for point source
- Sound intensity: I=W/4*pi*r^2, I=intensity, W=power source, r=distance from source
I=W/2*pi*r^2(hemispherical)
P=k/r, P=SPL, k=constant, r=dist
Critical distance: direct and reverberated sounds are same amplitude
Modal resonances…
Chp. 4
psychoacoustics: Not an exact science
Threshold of hearing: 50% people can hear, 50% can't
Outer: pinna+auditory canal.  auditory canal terminated by tympanic membrane(ear drum).  Pinna imprints directional information.  Ear canal increases loudness.  Resonance of 12dB @4K, smaller@9K.  Highest sensitivity to mid-range speech freq
Middle: air filled cavity w/hammer(malleus), anvil(incus), and stirrup(stapes).   Malleus attached to ear drum, stapes to oval window.  Form mechanical connection between eardrum and fluid of inner ear.
Inner: Auditory nerve sends electrical impulses to brain.  Leverage or osssicles+area of ear drum and oval window match impedance of air to fluid.  Vibration of oval window excites sensory hair cells which direct signals to brain.  
Fletcher Munson: Equal loudness counter, shows how loud SPL must be to sound equally loud to 1K reference. Phon-loudness.  Sones-subjective loudness
-Bandwidth, length of sound effect loudness.
-Subjective pitch: mel.
-By playing overtones, diff in overtones will be heard (fundamental)
-Binaural localization:Diff in intensity, arrival time, filtering create stereo image
-First wave front creates perception of direction
-Haas:Ear integrates all sound in first 50msec, giving perception sound is from earlier source
Franssen:Sound dies out will still be heard
Reflected delay=(reflected path-direct path)/1130
- Head related transfer function
Chp. 5
 Voiced (vocal chords), constriction (fricative), build of pressure(plosive)
-1) Sound produced in vocal tract, 2) pass through tract, which is filter, with formants as resounances.  3. Output shaped by resonance of vocal tract 
Total harmonic distortion= (root e2^2_e3^2…+en^2)x100/e0
Formants: Groups of overtones @ same fundamental
Chp. 6
Angle of incidence=angle of reflection, Parallel surfaces produce flutter, energy lost @ each reflection, pressure@reflective surface double incident wave, convex spreads sound, concave/parabolic focuses sound.  Parallel surfaces create standing waves
dist btw walls=wavelength of standing waves
mean free path: average distance sound travels between reflected surfaces
MFP: 4V/S v=volume s=surface area 
Chp. 7
How sound deals with obstacles
1) Object impeding sound: Low frequencies travel around object, high frequencies are blocked.  Easier to bend around smaller objects.  Acoustic shadow behind barrie
Large opening allow sound to pass (shadowed), small opening create appearance of point source at opening.  
2) Slit: High frequencies pass through but not low frequencies
Human head blocks 1K-6K.  Speaker cabinets also cause diffraction
Chp. 8 
Refraction: Path of propagation of a wave changes as a function of change in a medium.  Happens with light.
Solids: Rays perpendicular to wavefronts.  Air: faster in warm than cool, can be carried by wind.  Ocean: Vertical refraction, not as much horizontal.  speed decreases w/temp drop, increases again with pressure rise.
Most present in  sound with fog, temperature gradients have effect at outdoor concerts 
Chp. 9 
 Perfectly diffuse: Sound from all directions same amount in every part of room.  No freq, spatial irregularities, no beats, decay perfectly exponential, reverb time const in room, decay equal for all freq, not directionally dependant
Decay beats: smoothness increases as freq increases
dual exponential: 2 slopes
spatial uniformity - spatial variations of RT related to diffusion of space
absorbent in patterns-absorptive material better in patches
convex good for diffusion, concave bad
Chp. 10
Comb filtering: In small spaces there will be comb filtering effects due to parallel surfaces
f1 = C/2L, f2 = 2C/2L = C/L, fn = nC/2L
- Constructive/destructive interference do to signals in or out of phase being summed
- Only for signals with distributed energy(noise)
- Comb filtering has resonances at integer multiples.
- Phasing of particular frequencies based on room size creates peaks and nulls
- peaks: f=n/t, nulls: f=n/2t
- Larger delay=more peaks&nulls=less spacing=less noticeable.  Larger rooms have less audible comb filtering than small rooms
- Width of comb peak must be larger than critical band of human ear for given frequency to be audible
- More audible at low frequencies due to smaller critical bands
- Can occur in stereo speaker or mic placement
Examples: mic and floor, spaced mics, bleed on microphones, spaced loudspeakers, 3 way crossover, flush mounting mic
- This is why loudspeaker placement for near field monitoring is important
Longest sounding wave: Twice length between walls
Chp 11
Growth: Sound takes time to build to final level and reflections arrive to listener.  In practice this is usually instantaneous.
Decay: Components continue to reflect after source stops until all energy is lost.  Rate is exponential.  
Both are stepwise but can be drawn exponentially due to number of components
Calculated by RT60 (time for signal to drop 60 dB from peak)
Background noise may effect these calculations
Sabine: RT60=0.049V/A, v=volume, a=absorption
1) Direct sound 2) early Reflections 3) Reverb/Wash/Diffuse Sound
-Factors: Size of room, absorption coefficients, parallel walls, people in room
Measuring techniques: Impulse response (spark, pistol, balloon), sine sweep, steady state(pink noise), etc
- Normal modes: frequencies where energy is accentuated due to room dimensions
- Decay times will vary by frequency, bigger problem in small rooms
- Band passed noise or sine sweeps needed to get full reverb characteristic
- Acoustic coupling: openings to other rooms may cause a second exponential decay
- Electroacoustically coupled: Reverb characteristic of recorded sound will interact with reverb characteristic of room to create a possibly longer decay
- Speech: Excessive reverb lowers intelligibility of consonants.  Tradeoff is dead rooms  do not boost gain of speech enough.
- Studios and speech require more dead spaces, classical music requires more reverb, as well as bass rise for warmth.  
- Initial Time-Delay Gap (predelay): Time between direct and reverberated sound, gives info on size of hall.
- Artificial Reverberation- Needed for studio recordings, goal to mimic music halls without distorting spectrum.  Digital reverb created by different patterns of feedback delay.